1. The field of art to which the invention pertains comprises the art of measuring and testing of fluid pressures.
2. By and large the majority of better quality pressure sensitive instruments, such as the pressure gauge for measuring fluid pressure, employ a geared movement for translating Bourdon tube tip travel to an output utilization such as a readout pointer. These movements are well known and have been used commercially for many years. Typically, instruments of that type have a condition responsive element such as a Bourdon tube or the like providing arcuate deflection in response to condition changes to which the element is sensitive. In a common construction, as would be utilized in a pressure gauge, the geared movement is comprised of levers and gearing operably responsive to arcuate motion of the element for driving an output shaft supporting a rotatable pointer relative to a fixed dial plate. The dial graduation opposite the pointer position is indicative of the measured pressure value with which the instrument is being operated. Exemplifying such movements is the disclosure of U.S. Pat. No. 3,690,181 in which an elongated link connects the arcuate tail end of a pivotted segment gear with the free tip of the Bourdon tube. The segment gear in turn meshes with a pinion secured on the pointer shaft.
For connecting the link and segment gear it has been usual to employ screw and nut fasteners which have proven surprisingly difficult to handle because of the relatively close working conditions in which they must be installed. It is quite common for one or other of the screw or nut to be dropped more than once in the course of assembly. A captive nut for those purposes is disclosed in U.S. Pat. No. 3,690,181, supra. Further contributing toward the difficulty is that the point of connection between the link and segment gear frequently comprises the focal point for calibrating the instrument. This, therefore, may require disassembly and reassembly of the previous made connection for varying the distance between the point of connection and the pivot axis of the gear during a pressure test in order to ensure readout accuracy of the instrument. Similar complications can arise from replacement of a worn link or where necessary to replace one link with another of different length to obtain proper linearity in calibration. Such changes in calibration can involve nut displacements or adjustments on the order of 0.001 inches for gauges operative at one-half to one-quarter of one percent accuracy.
Whether for initial assembly purposes, calibration, link replacement or whatever, the difficulty and assembly time involved in joining the link to the segment gear have long been regarded as disproportionate to other aspects of the manufacturing operation. Despite recognition of the foregoing, a construction for greatly simplifying and reducing the previous expenditures of time and effort has not heretofore been readily known.